1. Field of the Invention
The present invention relates to a dewatering device of a machine for the production and/or processing of a material web, e.g., a paper web or a cardboard web, in which the material web is guided together with at least one screen through a nip which is elongated in the web travel direction. The nip is formed between a circulating flexible continuous belt, which is supported by a saddle, and an opposite surface. The present invention is also related to a glazing device of a machine for the production and/or processing of a material web, e.g., a paper web or a cardboard web, in which the material web is guided between a nip formed between a heated roller and a mating roller.
2. Discussion of Background Information
A dewatering device of the above mentioned type is known, e.g., from DE 197 23 163 A1. It is also known to perform the dewatering between two metal belts of which one is heated and the other is cooled. Moreover, originating from the heated belt, a paper web, a fine screen, and a coarse screen are arranged toward the cooled belt. Arrangements are also known in which the paper web and the screens are guided over a cooled or heated cylinder. Around the cylinder a metal belt is looped which is heated in the case of a cooled cylinder and is cooled in the case of a heated cylinder. The paper web always sits close to the heated surface. Between the paper web and the cooled surface there is at least one screen, usually a fine screen, which is provided close to the paper web and a coarse screen which is located close to the cooled surface. In all of these arrangements, pressure is transmitted during the dewatering process by a pressurized cooling and/or heating medium in the form of a gas or a liquid through an airtight surface such as, e.g., a metal belt to a sandwich formed by the two surfaces of paper, fine screen, and coarse screen (see, e.g., DE-A-26 57 041, FIG. 10; DE-A-32 03 571, FIG. 11; DE-A-35 32 853, FIG. 12).
However, the pressurized liquid requires very expensive constructions concerning the sealing and due to uncompensated forces. A change in the structure pressure applied can only be accomplished with several pressure chambers, which again increase the constructive expense.
Also there are arrangements known in which, during the dewatering process, the pressure is produced mechanically by one or more saddle presses which are pressed against a heated cylinder. In this way, it is possible to reduce the constructive expense necessary for production of the structure pressure and the pressure profile can be predetermined, within certain limits, by the selection of the form of the saddles (see, e.g., EP-A-0 890 675, FIG. 13). However, if only one saddle is used it results in a length of only about 200-300 mm, which is very short. If several saddles are used, the paper is always relieved of pressure between each saddle. This does not allow the construction of a continuous process because the steam pressure inside of the paper must be reduced to the outside pressure after each nip in order to avoid destruction of the paper.
Furthermore, there are also solutions known in which the structure pressure is produced by several pressure rollers against a heated cylinder. Here, too, a continuous process of a structure pressure cannot be created over a longer period of time (cf., e.g., U.S. Pat. No. 5,787,603, FIG. 14).